1. Field of the Invention
This invention relates to new and useful improvements in systems and apparatus for removing gas from drilling mud.
It is particularly concerned with a system including a vacuum tank of improved construction for removing poisonous, explosive gas entrained in drilling mud, and is further concerned with apparatus and control features associated with such a system.
2. Brief Description of the Prior Art
In drilling oil wells, it has long been standard practice to use drilling muds for the purpose of cooling and lubricating the drill bit, removing cuttings from the hole, lubricating the drill pipe, providing cake or seal lining for an exposed formation hole, and as a controllable hydraulic head or load for prevention of premature flowing of the well. Drilling muds are made heavier by addition of pulverized barites or barium sulfates.
As the hole goes deeper, greater earth rock pressures are encountered and thus greater oil or gas pressures when petroleum strata are reached. It is standard practice to carry surplus weight in the drilling mud as a safety factor for anticipation of abnormal gas pressures. As the hole deepens, the density of the mud is often increased to provide an added safety factor. An ideal system would be one where the mud is just heavy enough to suppress fluid flows from the formation being drilled, with only enough additional weight to offset the lightening effect of gases released from the formation. If the drilling mud is much heavier than the formation pressures encountered, then a serious hazard of mud loss to the formation arises. As a result, the driller can not just add a large surplus of weighting materials to his mud in order to prevent formation flows while drilling. If the mud is too light, hydrocarbons or salt water may flow from the formation and blow the mud column from the hole. If the mud is too heavy, it may break down a formation and flow into it instead of circulating back to the surface.
As drilling progresses, gases are picked up by the circulating mud. These gases may be petroleum gases or hydrogen sulfide or inert gases, such as, nitrogen or helium. The gases may be present initially as liquids under the pressures encountered at the drill bit, but as the mud rises to the top of the well with steadily decreasing pressure on it, these liquids turn into gases and expand and lighten the mud with the dissolved gases or gas bubbles formed in it. If the dissolved gases or gas bubbles are not removed and the mud recirculated, it picks up still more gas, making the mud even lighter, necessitating the addition of even greater amounts of weighting materials. Thus, the thorough removal of entrained and dissolved gases and lighter liquid hydrocarbons from the drilling mud is quite important in drilling oil or gas wells.
In the past, many techniques have been used for removal of gases from drilling muds. In earlier times, drilling muds were simply flowed through long troughs or ditches and were agitated by some means to facilitate removal gas. Many different types of apparatus have been designed for removal of gases from drilling muds but most have been discarded for one reason or another, usually a matter of economy or efficiency.
Erwin U.S. Pat. No. 2,748,884 discloses an apparatus for continuously degassing drilling mud including a degassing vacuum tank and jet nozzles for circulating the drilling mud.
Long U.S. Pat. No. 3,201,919 discloses a drilling mud degasser apparatus in which drilling mud is circulated into a vacuum tank along a helical path and withdrawn and recirculated into the well.
Griffin U.S. Pat. No. 3,241,295 discloses a drilling mud degasser having various valves and controls for controlling the rate of mud flow into a degassing tank.
Burnham U.S. Pat. No. 3,362,136 discloses a degasser apparatus for drilling muds in which the drilling mud moves on a helical shelf downward into a vacuum tank.
Bournham U.S. Pat. No. 3,895,927 discloses a drilling mud degasser apparatus having baffle plates in a vacuum tank over which thin films of mud are degassed.
Brunato U.S. Pat. No. 3,898,061 discloses a degasser apparatus which breaks up the mud-gas emulsion by a combination of mechanical action and vacuum and disposes of the separated gas at a location remote from the working area.
Griffin U.S. Pat. No. 4,010,012 discloses a drilling mud degasser system which removes gas from drilling mud without allowing it to escape to the atmosphere before the gas is treated to prevent contamination. The drilling mud flows downward into a vacuum degassing tank and gases removed overhead and degassed mud is removed from the bottom of the degasser tank.